1. Field of the Invention
The invention relates to a medical implantable lead adapted to be inserted into a human or animal body and attached, with its distal end, to tissue inside the body, of the type having a rotatable helix in the distal end that can be screwed into the tissue, the helix being adapted to serve as an attachment of the lead to the tissue as well as to serve as a conductor for conducting of electrical signals to the tissue through electrical conducting surfaces on the helix, wherein the surfaces of the helix being partly insulated to restrict the conducting of signals between the helix and the tissue to desirable regions.
The invention also relates to a method for manufacturing of a helix for a medical implantable lead.
2. Description of the Prior Art
A medical implantable lead of the above kind may be used for different purposes, such as for connection to a pacemaker for monitoring and pacing the activity of a human heart, or for use as a nerve stimulator, or for connection to a diagnostic device for monitoring and stimulating the activity of an arbitrary organ in a human or animal body.
Such a diagnostic and therapeutic device is often implanted into the body to perform its function during a long time. In such cases the electrical power source for power supply to the lead, is in form of at least one battery positioned in the device. In order to prolong the battery life, and hence extend the time interval between each replacement of the implanted device, it is advantageous to restrict the power consumption as much as possible. The current drain from the lead has a great influence on the overall power consumption and if the transition impedance from the helix in the lead to body tissue is increased, the current drain will be reduced. One way to achieve this is to restrict the electrically conductive surfaces on the helix by applying an insulating layer on parts of the surface thereof.
In U.S. Pat. No. 6,501,994 and United States Patent Application Publication No. 2004/0133259 the above problem has been recognized and consequently the implantable leads disclosed in these publications, are provided with helixes whose surfaces have been provided with an insulating coating over a portion of the helix. However, the current drain from these helixes is still considerable, and it would be favorable to further restrict the current drain to allow a more effective utilization of the electrical power.
U.S. Pat. No. 5,476,502 discloses a defibrillation electrode in the shape of a helix that, although a part of the inside of the helix is provided with an insulating layer, is designed to have a conducting surface that is as large as possible an hence with a low impedance.